1. Technical Field
The present invention relates to a hydraulic circuit for hydraulic equipment used in various types of construction work, such as hydraulic shovels.
2. Background Art
Some hydraulic equipment for construction work is arranged to control pressurized oil fed to a plurality of hydraulic actuators, using their corresponding control valves. Switching means for such control valves include pilot-operated means, which use pilot pressurized oil fed to control valves, and other means, for example, manual, mechanical, and electrical means.
Since control equipment for such means, including operating levers, is sometimes operated unexpectedly against the operator's will, a safety locking mechanism needs to be installed in hydraulic equipment to prevent hydraulic actuators from operating accidentally. To form such a safety locking mechanism, conventional pilot-operated means have safety valves installed in pilot oil lines between pilot pressurized oil sources and pilot valves, switching pilot pressurized oil feed to control valves. When a safety valve is closed, pilot pressurized oil is not fed to a control valve, so that it cannot be switched to their pressurized oil feed position. However, when the operator unlocks the safety lever in the operator's seat, for example, the safety valve opens, thus allowing pilot pressurized oil to be fed to the control valve. The other means mentioned above have mechanical locking devices attached to the control equipment, by use of which devices the operator locks or unlocks the control equipment.
Locking mechanisms for switching means other than pilot-operated means have a problem of a locking device being required by the individual control equipment. What is worse, operating such a locking device is troublesome because it needs to be operated every time locking or unlocking is done. To solve these problems, the idea has been proposed that locking devices for switching means are interlocked so that locking and unlocking can be done using switches. Mechanisms based on the idea, however, also need locking devices for their individual control equipment, which consist of many parts and are complex in structure and costly. This is a problem which the present invention is intended to solve.
Another problem with conventional switching means is that safety valves for pilot-operated means and those for other means use different locking mechanisms.